Margaret Edson’s 1999 Pulitzer Prize-winner is a heady and thoroughly unsentimental work, exploring the meaning of mortality through Vivian’s brutal struggle with cancer (and its treatment), juxtaposed with wisdom and mysteries gleaned from the 17th-century poetry of John Donne.

It’s a play driven by sometimes dizzying writing, but to really work it needs to be grounded in a fearless lead performance, and that’s what Smyth provides at Lamb's Players Theatre, where she's an associate artistic director.

Her work can be hard to watch at times, as the ever-proud Vivian descends into an abyss of physical pain and philosophical doubt. But Smyth not only has a way with the playwright’s complex, rapid-fire flights of language, but conveys a sense of utter steeliness, of looking weakness straight in the face and bringing it to its knees.

She also has a sure grasp of that (yes) withering wit — demonstrated both as Vivian addresses the audience directly (she serves as the narrator of her own tale, informing us with a smile right at the top that “I think I die in the end”) and in dialogue scenes with other characters.

At one point, after the draining, potentially deadly experimental therapy she’s undergoing causes her to utter an epithet or two, Vivian acknowledges to the audience: “You may notice that my vocabulary has taken a turn for the Anglo-Saxon.”

When Vivian’s ex-student Jason (an amusingly officious Jason Heil), who’s now an aspiring medical researcher and one of her doctors, asks what she does for exercise, she replies: “Pace.”

That’s an insight into how driven the brilliant Vivian is, although a minor weakness of the play is it never quite explains how and why she’s so completely alone in life that she receives not a single visitor until the end. (Donne famously wrote that “No man is an island,” but Vivian is so cut off from other people she seems as remote as an asteroid.)

Robert Smyth, the producing artistic director at Lamb’s (and Gilmour Smyth's husband), directs the 90-minute, one-act play with a strong sense of rhythm, and the supporting cast does solid work, including Cynthia Gerber as the sweetly caring nurse Susie, Jim Chovick as the plainspoken head doctor Kelikian, Sylvia M’Lafi Thompson as Vivian’s onetime mentor E.M. Ashford, and Kaja Amado Dunn, Bryan Barbarin and Caitie Grady in multiple roles.

In a play full of paradoxes, it’s fitting that the generally unsparing “Wit” winds down with a moment of tenderness, as Thompson’s character arrives to comfort Vivian. And if the ending is not a surprise, the way it’s portrayed is still pretty sublime.